#include <stdio.h>

int main(int argc,char *argv[])
{
    int i,n,sum;
    
    while(scanf("%d",&n) != EOF)
    {
        sum = 0;
        for(i = 1;i <= n;i++)
        {
            sum += i;
        }
        
        printf("%d\n\n",sum);
    }
    
    return 0;
}













































































